Synthesis, Characterization, and Theoretical Studies on Heterobinuclear (p-cymene)Os(μ-pz)₂M (M = Ir, Rh; Hpz = Pyrazole) Complexes

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Abstract

The cationic compounds [(η6-p-cymene)OsCl(Hpz)2]A (A = Cl (1), BF4 (2)) have been prepared by treating the dimeric [{(η6-p-cymene)OsCl}2(μ-Cl)2] with pyrazole (p-cymene = p-isopropylmethylbenzene, Hpz = pyrazole). Compounds 1 and 2 are precursors to new heterobinuclear complexes of stoichiometry [(η6-p-cymene)OsCl(μ-pz)2M(COD)] (M = Ir (3), Rh (4); COD = 1,5-cyclooctadiene). Carbonylation of 3 and 4 produces the dicarbonyls [(η6-p-cymene)OsCl(μ-pz)2M(CO)2] (M = Ir (5a), Rh (6)) or, in the presence of NaBPh4, the cationic tricarbonyls [(η6-p-cymene)Os(CO)(μ-pz)2M(CO)2]BPh4 (M = Ir (7), Rh (8)). Complex 5a in methanol isomerizes to the metal−metal-bonded compound (5b) (first-order kinetics in 5a; kobs = 3.8 × 10-4 s-1 (room temperature), ΔH⧧ = 93 kJ mol-1, ΔS⧧ = 7 J K-1 mol-1). The molecular structures of [(η6-p-cymene)OsCl(μ-pz)2Rh(CO)2] (6) and [(η6-p-cymene)Os(CO)(μ-pz)2Rh(CO)2]BPh4 (8) have been determined by X-ray diffraction methods. In both cases, the molecules contain (η6-p-cymene)Os and Rh(CO)2 moieties bridged by two pyrazolate groups. The osmium−rhodium distances, 3.6231(5) Å (6) or 3.7012(6) Å (8), exclude any direct intermetallic interaction. The metal−metal-bonded halide carbonyl complexes (X = Br (9), I (10)) and (12), as well as the OsRh compound [(η6-p-cymene)OsBr(μ-pz)2Rh(CO)2] (11), have been prepared by metathetical reaction on the corresponding dicarbonyls 5a,b and 6 with sodium halides. The molecular structures of 10 and 12 have been elucidated by diffractometric means. The metal−metal distances, 2.7196(6) Å (Os−Ir, 10) and 2.6936(9) Å (Os−Rh, 12), confirm the presence of metal−metal bonds. In the solid state, complex 12 crystallizes as a dimer of two dinuclear moieties through an asymmetric diiodide bridge. A theoretical study of the related RuIr dicarbonyl chloride isomers [(η6-p-cymene)RuCl(μ-pz)2Ir(CO)2] (13a) and (13b) is also reported.

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